It is known that metallic pigment, especially aluminum powder or aluminum flakes, is formulated into paint to provide metallic finishes. Most metallic paints are organic solvent type. Due to the problems of environmental pollution, waterborne paints are now proposed.
However, when a metallic pigment is incorporated into waterborne paint, the metallic pigment is reacted with water to generate hydrogen gas which is often associated with explosion danger. This problem is especially serious in the automotive industry in which paint is stored in a closed container for a long period of time before use.
In order to obviate this problem, it is proposed in Japanese Kokai Publication 168663/1983 that the metallic pigment is treated with a particular organic phosphate to make its surface hydrophobic. This method, however, often aggregates metallic pigments and adversely affects the smoothness and metallic appearance of the coating, thus deteriorating adhesive properties. These defects are improved by using a surfactant in a large amount, but it adversely affects water-resistance.